Labelled 2SC4578, the 104 KB PDF is indexed as a schematic, though its name matches a single semiconductor part, so it is probably a datasheet. The JIS 2SC prefix marks an NPN bipolar transistor of the high-frequency category. No extra details appear in the name. Use it to verify which pin is base, collector or emitter, check breakdown voltage and collector current, and review dissipation limits. Compare the body marking on the actual component before relying on the document.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @cyberlanelectonik. Enginerys does not host this file.
How to open a .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.